“By the Rhamda?”

“Undoubtedly.”

“Who is he?”

Hobart smiled.

“How do I know?  Where did he come from?  If we knew that, we would know everything.  ‘A phantom,’ so Watson says.  If so, it only strengthens our theory.  It would make a man and matter only a part of creation.  Certainly it would clear up a lot of doubts.”

“And the ring?”

“It controls the Blind Spot.”

“In what way?”

“That’s for us to find out.”

“And Watson?  He is in this land of doubt?”

“At least he is in the Blind Spot.  Let me try the ring.”

He struck a match.

It was much as it had been in the restaurant, only a bit more startling.  Then the blue faded, the colour went out, and it became transparent.  For a moment.  There was an effect of space and distance that I had not noted before, almost marvellous.  If I could describe it at all, I would say a crystal corridor of a vastness that can scarcely be imagined.  It made one dizzy, even in that bit of jewel:  one lost proportion, it was height, distance, space immeasurable.  For an instant.  Then the whole thing blurred and clouded.  Something passed across the face; the transparency turned to opaqueness, and then—­two men.  It was as sudden as a flash—­the materialisation.  There was no question.  They were alive.  Watson was with the professor.

It was a strange moment.  Only an hour before one of them had been with us.  It was Watson, beyond a doubt.  He was alive; one could almost believe him in the jewel.  We had heard his story:  “The screen of the occult; the curtain of shadow.”  We had seen him go.  There was an element of horror in the thing, and of fascination.  The great professor!  The faithful Watson!  Where had they gone?

It was not until the colour had come back and the blue had regained its lustre that either of us looked up.  Could such a thing be unravelled?  Fenton turned the stone over thoughtfully.  He shook his head.

“In that jewel, Harry, lies the secret.  I wish I knew a bit more about physics, light, force, energy, vibration.  We have got to know.”

“Your theory?”

“It still holds good.”

I thought.

“Let me get it clear, Hobart.  You say that we catch only certain vibrations.”

“That’s it.  Our eyes are instruments, nothing else.  We can see light, but we cannot hear it.  We hear sound, but we cannot see it.  Of course they are not exactly parallel.  But it serves the point.  Let’s go a bit further.  The eye picks up certain vibrations.  Light is nothing but energy vibrating at a tremendous speed.  It has to be just so high for the eye to pick it up.  A great deal we do not get.  For instance, we can only catch one-twelfth of the solar spectrum.  Until recently we have believed only what we could see.  Science has pulled us out of the rut.  It may pull us through the Blind Spot.”